Systems for automatically controlling the direction of a beam produced by a headlight of a vehicle to be controlled are important to provide adequate light for the driver without dazzling other persons, such as the driver of a proceeding vehicle that the controlled vehicle follows.
An example of such control systems is disclosed in WO 2001/070538.
The control system disclosed in the WO publication is configured to control the direction of a beam produced by a headlight of a vehicle to be controlled on the basis of the distance of a preceding vehicle relation to the controlled vehicle.
Specifically, when the distance of the preceding vehicle with respect to the controlled vehicle becomes short, the control system is configured to change the direction of the beam downward. On the other hand, when the distance of the preceding vehicle with respect to the controlled vehicle becomes long, the control system is configured to change the direction of the beam upward.
The WO publication however may not sufficiently describe definite algorithms for changing the direction of the beam upward and downward.
Thus, the control system disclosed in the WO publication may change the direction of the beam excessively upward depending on the increase in the distance of the preceding vehicle with respect to the controlled vehicle; this may dazzle the driver of the leading vehicle.
The control system disclosed in the WO publication may also change the direction of the beam excessively downward depending on the reduction in the distance of the preceding vehicle with respect to the controlled vehicle; this may cause an unirradiated region between the preceding vehicle and an irradiated field of the beam. The unirradiated region may have poor viewability for the driver of the controlled vehicle due to low light.